In recent years, along with the increasing size of casings of steam turbines and the increasing temperature of the operating conditions, the length and the diameter of rotors tend to become larger and larger. This considerably increases a thermal elongation difference due to the relative thermal expansion of the turbine casing (inner casing) and the rotor, generated when the steam turbine is started up and is operated with a low load. For example, in a low-pressure turbine 5b disclosed in PTL 1, a thermal elongation difference due to the relative thermal expansion of a rotor and an inner casing of the low-pressure turbine 5b, which is the farthest from a thrust bearing 18 or 18a, is increased considerably.
Thus, instead of using a casing position adjusting apparatus 18 disclosed in PTL 2, a recently proposed steam turbine casing position adjusting apparatus 80 moves an inner casing (turbine casing) 21 in the axial direction by using actuators 20 having rods 26 that advance and recede in the axial direction of a rotor 23, as shown in FIG. 37 or 38, thus reducing a thermal elongation difference due to the relative thermal expansion of the inner casing 21 and the rotor 23.